Trans‐regional transport of haze particles from the North China Plain to Yangtze River Delta during winter

According to atmospheric modeling and satellite observations, cold fronts can cause trans‐regional transport (TRT) of haze particles from the North China Plain (NCP) to Yangtze River Delta (YRD) in winter. However, compositions and aging of haze aerosols during the TRT have not been studied. We showed the TRT PM_2.5 dominated by organic matter (OM) (30%) and secondary inorganic ions (36%) in the NCP and 29% and 60% in the YRD. Following the TRT, abundant spherical primary OM particles (i.e., tarballs) (71% by number) mainly from residential coal burning in rural areas of the NCP unexpectedly occurred in the YRD. The inert tarballs display similar sizes (∼300 nm) and O/C ratios (∼0.15), but the mixture of nitrate, sulfate, and secondary OM as the coatings completely convert the hydrophobic tarballs into hydrophilic ones in the TRT. The aging and transport of tarballs from the NCP to YRD further indicate that the TRT not only brought various trace gases (e.g., CO, SO₂, NO_x, and VOCs) but also carried large numbers of nanosized primary particles (e.g., tarball, metal, fly ash, and soot) with secondary coatings over 1,000 km. The findings suggest that these many nanosized tarballs containing brown carbon and highly toxic species in the NCP influence regional climate and human health in northern and eastern China, which needs more attention. Although the NCP and YRD have different energy consumption structures in winter and are two isolated administrative regions, we emphasize the need for a coordinated cross‐regional emission reduction strategy for TRT haze control.